1. Field of the Invention
The invention relates to a novel process for preparing substituted 4-alkoxycarbonyl-3-aminothiophenes which are known as intermediates for active ingredients in agriculture, especially for substituted, herbicidally active thienylaminocarbonyltriazolinones (cf. WO 01/05788).
2. Description of Related Art
It is known that substituted 4-alkoxycarbonyl-3-aminothiophenes can be prepared by oxidation with hydrogen peroxide and subsequent acidic workup (EP-A 331 919). However, the achievable yields in these processes are not entirely satisfactory. It has further been stated that 4-alkoxycarbonyl-3-aminothiophenes are prepared by reacting 3-oxatetrahydrothiophenes with an acid addition salt of hydroxylamine, and the resulting oximes can be treated with an acid (DE-A 27 37 738) or converted in situ to the corresponding amine hydrochlorides. However, a disadvantage of this reaction is the observed occurrence of decarboxylated amine as an undesired by-product, complicated purification and the need to use the hydroxylamine acid addition salt in a large excess.